1. Field of the Invention
The present invention relates to a semiconductor device having a capacitance element and method of producing the same, and particularly to a technology to shorten a production process of the semiconductor device.
2. Description of the Related Art
A capacitance element is used for a capacitor of a delay circuit and an integration circuit of an LSI, and a DRAM cell. Conventionally, a method to make the capacitance element in the semiconductor device is, for example, as follows.
Initially, a selective oxidation process using a LOCOS method is performed. As a method used when a selective oxide film is formed by the LOCOS method, so called a PBL method (Poly-Buffered LOCOS method) is well known. The PBL method is a method in which, in order to reduce a bird's beak, previously an insulation film (hereinafter, called pad oxide film) and polycrystalline silicon layer (hereinafter, called pad.polycrystalline silicon layer) are formed between an oxidation resisting film and a semiconductor substrate as a buffer layer. Then, the oxidation resisting film such as silicon nitride film (Si.sub.3 N.sub.4 film) is formed on this upper layer, and by conducting thermal oxidation, an element separation film is formed. After that, the pad polycrystalline silicon layer, the silicon nitride film, or the like, are removed, and after that, a dummy oxide film is formed by thermal oxidation.
Then, through the dummy oxide film, impurities such as phosphorous or the like, are ion-implanted into the silicon substrate, and an impurity layer is formed. The dummy oxide film is the buffer film for the ion implantation.
Then, the dummy oxide film is removed, and thermal oxidation is performed again, and a gate oxide film is formed on the impurity layer. This is a capacitance oxide film, and at the same time, a gate oxide film of a MOSFET.
Further, the polycrystalline silicon layer is formed on the gate oxide film. In this manner, the capacitance element formed of the gate oxide film and the polycrystalline silicon layer is formed.